The inability to deliver therapeutic agents to chronic lymphocytic leukemia (CLL) cells in vitro or in vivo is a fundamental impediment to any drug or gene therapy for this disease. For CLL, gene therapy approaches to deliver immunostimulatory gene products to CLL cells hold great promise for treating this disease, however, current gene therapy vectors are not optimal for this application. In particular, most gene therapy vectors fail to effectively deliver genes into CLL cells making ex vivo approaches inefficient. By contrast, most vectors mediate robust, but non-specific gene delivery to many non-CLL cells in the body. This inability to deliver genes into CLL cells combined with a robust ability to deliver genes into the liver and immune cells makes current vectors unsafe for in vivo applications against CLL. Given that current vectors are inadequate for these CLL applications, this project proposes to develop CLL-targeting ligands and vectors to increase CLL transduction in vitro and mediate CLL-specific gene delivery in vivo. Towards this goal, the project will pursue the following Specific Aims: Specific Aim 1: To generate cell-targeting ligands against human CLL cells. Specific Aim 2. To translate CLL- targeting ligands onto adenovirus gene therapy vectors and test for improved CLL transduction in vitro. Specific Aim 3. To optimize the affinity and specificity of CLL-binding and CLL- targeting peptides. Specific Aim 4. To test the ability of CLL- targeting adenoviral vectors to mediate CLL-specific gene delivery in mouse xenografts of human CLL cells. We will use our peptide libraries to select targeting ligands against a panel of primary patient CLL cancer cells with the rationale that ligands generated here can be translated directly into clinical application against human tumors. As targeting ligands are identified, they will be optimized and tested for their ability to increase CLL transduction and CLL-specific transduction by adenoviral gene therapy vectors in vitro. Promising targeting vectors will then be tested in vivo in mouse xenografts for their ability to mediate human CLL-specific transduction in the context of a living organism. If successful, this work will lay the foundation for future applications of these CLL-targeting ligands and vectors for gene therapy for CLL patients through the clinical arm of the Center for Cell and Gene Therapy at Baylor College of Medicine.